Why Is Further Treatment Needed?
PVC production using chlor-alkali processes can generate wastewater containing mercury, a highly toxic and persistent heavy metal that may accumulate in the food chain. Chemical precipitation, particularly sulfide precipitation, can significantly reduce Hg concentrations, but residual mercury may remain and require further treatment before discharge.
Chelating ion-exchange resin can provide a further treatment step. Its functional groups, immobilized within a porous polymer matrix, bind mercury ions and help separate them from the wastewater stream.
TFI-CLS047 Resin Characteristics
TFI-CLS047 is a macroporous polystyrene-based thiol chelating resin developed for selective mercury adsorption and valuable-metal recovery from industrial effluent. Its thiol (–SH) functional groups have a strong affinity for soft metal ions such as Hg²⁺.
| Parameter | Characteristics |
|---|---|
| Matrix | Macroporous polystyrene |
| Functional group | Thiol |
| Selectivity | Hg > Ag > Cu > Pb > Cd > Ni > Co > Fe > Ca > Na |
| Operating pH range | pH 2–10 |
| Total capacity | ≥3,0 mmol/mL |
| Hg residual target | Below 5 ppb |
Metal affinity ranking
- 1HgMercury
- 2AgSilver
- 3CuCopper
- 4PbLead
- 5CdCadmium
- 6NiNickel
- 7CoCobalt
- 8FeIron
- 9CaCalcium
- 10NaSodium
Read from left to right and continue on the next row: resin affinity decreases from mercury to sodium.
The macroporous structure provides a large surface area and accessible functional groups, supporting mercury capture at low concentrations.
Mercury Removal Mechanism
Under suitable wastewater conditions, dissolved mercury may be converted to the ionic form Hg²⁺ before contacting the resin. Hg²⁺ then coordinates with thiol groups on the resin to form a stable complex, while treated water exits the column.
The binding process can be represented schematically as follows:
Here, R–SH represents a thiol group on the resin matrix. Its high affinity for Hg²⁺ supports selectivity even when other metal ions are present in the wastewater.
PVC Wastewater Treatment Process
A typical treatment configuration combines upstream treatment with ion exchange:
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Wastewater collection and equalization
Stabilizes flow rate and Hg concentration.
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pH adjustment and pretreatment
Conditions mercury into a form that can be captured by the resin and removes suspended particles.
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Chemical precipitation
For example, sulfide precipitation can reduce the incoming mercury load.
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Filtration or clarification
Protects the resin column from suspended solids.
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TFI-CLS047 ion-exchange column Polishing
A polishing step intended to achieve very low Hg concentrations.
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Effluent monitoring
Conduct periodic testing for total and dissolved mercury.
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Spent resin regeneration or management
Manage in accordance with applicable hazardous-waste requirements.
This approach is described for wastewater containing approximately 0.01–5 mg/L mercury. Upstream chemical treatment should be selected based on the actual wastewater characteristics and required effluent target.
Performance in the PVC Industry
A case study at a chlor-alkali-based PVC producer reported a TFI-CLS047 system operating at a flow rate of 6 tonnes per hour, continuously for 24 hours per day. The system used upstream chemical treatment followed by TFI-CLS047 resin as a polishing step.
- Flow rate
- 6 tonnes/hour
- Operation
- 24 hours/day
- Effluent Hg
- ≤1 ppb
The reported results indicate that effluent mercury remained at ≤1 ppb during the reported operation. Actual performance and compliance depend on wastewater chemistry, system design, operating conditions, and applicable discharge requirements.
Technical Advantages
- High selectivity for Hg²⁺Designed to retain selectivity in the presence of competing ions such as Cu, Pb, Cd, Ni, and Fe.
- Hg residual below 5 ppbThe stated target of less than 5 ppb may support stringent treatment objectives; confirm performance through testing on the actual wastewater.
- Broad pH range: pH 2–10Offers flexibility across different wastewater conditions, subject to validation.
- Suitable for continuous operationCan be considered for industrial-scale systems with appropriate design and monitoring.
- Potential for regeneration and reuseReuse depends on the selected regeneration procedure, wastewater chemistry, and verified resin performance.
Operation and Safety
System performance depends on wastewater pretreatment, pH control, flow rate, turbidity, and the presence of strong oxidizing agents.
Conclusion
TFI-CLS047 is a potential polishing option for mercury removal from PVC industry wastewater after precipitation or other physicochemical treatment. Its thiol functional groups and macroporous structure are intended to support selective mercury capture. Confirm suitability and achievable effluent concentrations with representative wastewater testing and a properly designed pilot evaluation.